Shutter mechanism for a video tape camera

ABSTRACT

A focal plane shutter for a video camera has a pair of disks rotated in the same direction about a common axis in synchronism with the raster scan blanking interval. The disks each have one or more openings which overlie one another to define a light admitting shutter aperture positioned to illuminate the video pickup device. The opening in at least one of the disks is counterbalanced during rotation by a recessed relief area which does not extend through the disk, or by a weighted plate attached to the disk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.562,233 which was filed on Dec. 16, 1983 (now U.S. Pat. No. 4,547,051).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to video cameras, and moreparticularly to shutter mechanisms for video cameras. More specifically,the invention relates to improved focal plane shutters for producingstop action or slow motion pictures without blurring, skewing ordistortion.

2. Description of the Prior Art

The capturing of physical images through video recording involves aprocess whereby light reflecting or emanating from objects within ascene is collected and converted into electrical energy, and thenmagnetically stored for replay at a later time. The typical video systemincludes an optical system comprising one or more high quality,color-corrected lenses for focusing an image on the photosensitivesurface of a video pickup device. Optical focusing is achieved by movingthe lense with respect to the pickup device or by moving the pickupdevice with respect to the lense. The light which reaches thephotosensitive surface of the pickup tube or other pickup devicerepresents the image of the scene being recorded.

The exposure or quantity of light reaching the pickup tube surface maybe controlled by varying the exposure time, by varying the size of thelense aperture or opening through which the exposure is made, or byvarying both exposure time and lense aperture size--all of which arerelated to one another through the principle of reciprocity. Theprinciple of reciprocity states generally that exposure time and lenseaperture size are inversely related and that an exposure of a givenquantity of light can be achieved by a wide variety of exposuretime/aperture size combinations. To vary the exposure time, rotary focalplane shutters are sometimes placed between the lense and the pickuptube or device. Prior art rotary focal plane shutters are discussed morefully below. To vary the lense aperture size, it is common to providethe optical system or lense with an iris diaphragm mechanism whichcomprises thin overlapping metal plates that can be adjusted to form anaperture of varying size. Such mechanisms are frequently calibrated in"f-stops".

Once the optical image reaches the video pickup it is converted into anelectrical video signal. The pickup is used to generate a train ofelectrical pulses representing the light intensities present in theoptical image which is or has been focused on the surface of the pickup.Each point or pixel of this image is interrogated in its proper turn bythe pickup, and an electrical impulse corresponding to the amount oflight at that point is generated. Usually the electrical impulses from aplurality of points are serially combined or concatenated to comprisethe video signal. In many pickup devices popular today, each point isinterrogated by an electron beam which is electrostatically ormagnetically deflected back and forth across a prescribed pattern(called a raster) on the glass target found on the inside of the pickupdevice. Electronic deflection circuitry generates electrical waveformswhich, when applied to deflection coils or the like, produce a linearscanning motion of the electron beam following the prescribed rasterpattern. To improve the image it is common to generate an interlacedraster, whereby all odd numbered lines are first sequentiallyinterrogated, followed by a vertical retrace of the beam to its point oforigin, and then all even numbered lines are sequentially interrogated.During vertical retrace the electron beam is swept, usually diagonally,from its termination point at the end of the last line in the rasterpattern or field to its origin point. During vertical retrace a blankingsignal is generated for a duration or blanking interval sufficient toallow the beam to sweep from termination point to origin point. Theblanking signal causes the pickup device to momentarily cut off itssignal output so that retrace lines are not visible when the image isviewed or replayed.

Most present day video pickups comprise electron tubes although thereare also solid state devices. Such electron tubes may be classifiedbased on the method of signal generation. In a non-storage tube, theonly light utilized in generating a signal is that light reaching aparticular point on the tube's light sensitive region while that pointis being scanned or interrogated. In a storage tube, on the other hand,an electric charge accumulates on the tube's light sensitive region ateach point during the interval between successive scans for laterinterrogation. Because the storage-type tube uses the electric chargesgenerated by the light during the comparatively long intervals betweensuccessive scans of the image, it is more efficient and more sensitive.Storage-type tubes are further classified according to whether the lightsensitive element is photoemissive or photoconductive. Whenphotoemissive materials absorb light they emit electrons. Whenphotoconductive materials absorb light their electrical conductivitychanges.

The "vidicon" tube is one such photoconductive storage tube which hasgained great popularity due to its small size and simplicity ofoperation. The vidicon is a storage-type tube in which the signal outputis developed directly from the target of the tube and is generated by alow velocity scanning beam from an electron gun. The target consists ofa transparent signal electrode deposited on the face plate of the tubeand a thin layer of photoconductive material, which is deposited overthe electrode. The photoconductive layer serves two purposes. It is thelight sensitive element, and it also forms the storage surface for theelectrical charge pattern that corresponds to the light image falling onthe signal electrode. The photoconductive material has a fairly highresistance when in the dark. Light falling on the material excitesadditional electrons into a conducting state, lowering the resistance ofthe photoconductive material at the point of illumination. In operation,a positive voltage is applied to one side of the photoconductive layervia the signal electrode. On the other side of the layer the scanningelectron beam deposits low velocity electrons in sufficient numbers tomaintain a net zero voltage. In the interval between successive scans ofa particular spot, the incident light lowers the resistance in relationto its intensity. With the resistance lowered, current flows through thesurface of the photoconductive layer and a positive charge is built upon the back surface of the layer; that positive charge is then helduntil the beam returns to scan the point. When the beam returns, asignal output current is generated at the signal electrode as thispositively charged area returns to zero voltage.

In order to provide low velocity electrons in a uniform manner, a finemesh screen is stretched across the interior of the tube near thetarget. The screen is energized to cause the electron scanning beam todecelerate uniformly at all points and to approach the target in aperpendicular manner. The beam is brought into sharp focus on the targetby longitudinal magnetic fields produced by focusing coils surroundingthe tube. The beam is made to scan the target in its characteristicraster pattern by varying magnetic fields produced by horizontal andvertical deflection coils also disposed about the tube.

Video systems of the prior art, including those using storage tubedevices, have been historically plagued with difficult and troublesomeblurring, skewing and distortion when used to produce slow motion orstop-action images. Slow motion and stop action images are createdduring playback by utilizing specially equipped video tape decks. Suchtape decks, however, can only produce images as clear and sharp as thevideo camera which produced them. If the video camera produces blurred,fuzzy or distorted images, then the taped image will also be blurred,fuzzy and distorted. These undesirable effects are most apparent duringslow motion or stop-action replay.

A prior art solution to the problem of blurred images is to interpose arotary shutter between the lense and pickup of an otherwise standardvideo camera. The rotary shutter of the prior art comprises a circulardisk provided with at least one matched pair of apertures spaced 180°apart about the circumference. The disk is rotated at a constant speedin use (typically 1800 rpm). The apertures are positioned about a locusbetween lenses and pickup so that for two brief intervals per diskrevolution, light images will illuminate the pickup tube. The aperturesare pie-shaped openings or segments bounded by radial lines emanatingfrom the center of rotation of the disk. Thus, by virtue of the factthat the pie-shaped apertures are paired and spaced 180° apart, 3,600individual or discrete exposures are made each minute at a rotationalrate of 1800 rpm. The exposures are timed to occur during the blankingintervals, hence each full raster interrogation produces a train ofelectrical impulses which represents the image exposed during a previousblanking interval. By using very short time intervals a fast movingobject, such as a rocket sled, or an athletic event, can be captured,stored and reproduced with less blurring or fuzziness than without theshutter. However, shutters of the prior art have been heretofore limitedto shutter speeds of no faster than 1/10,000 second. While this mightseem quite fast, in high speed motion studies, during athletic events,and so forth, there are numerous events which cannot be capturedsatisfactorily at this shutter speed.

Moreover, there has heretofore been an unsolved problem associated withfast shutter speeds. Too fast a shutter speed can effectively reduce theoverall quantity of light reaching the pickup to the point where thepickup cannot properly respond. One solution is to open the lenseaperture, if one is provided, to a wider f-stop--which has its owndrawbacks, among them being a degradation in depth of field. Anothersolution is to provide other, slower shutter speeds. Thus, prior artshutters are frequently provided with a plurality of different sizedmatched pairs of pie-shaped apertures, each pair corresponding to adifferent discrete exposure time or shutter speed. With such anarrangement, however, it is not possible to continuously vary theshutter speed. One cannot, for example, select a shutter speed betweentwo discrete speeds. Furthermore, in order to change shutter speedsusing prior art systems, it is necessary to first stop the rotatingshutter mechanism and lock it in place while indexing the mechanism to anew shutter speed. Varying the shutter speed while the shutter is inmotion (while recording a scene, for example) is not possible with priorart systems. Hence, such systems cannot be made to readily react totransient changes in light levels, such as might be caused by a passingcloud.

Another problem with prior art rotary shutter devices stems from the useof a pie-shaped shutter opening. Video pickup tubes usually have arectangular format, e.g. 4:3 width-to-height ratio. To evenly illuminatea rectangular pickup surface the shutter aperture must be constructed tosweep across equal areas at equal rates on both sides of the diagonal ofthe rectangular surface. In other words, the rectangular pickup must beoriented so that one of its vertical or horizontal centerlines coincideswith the radial lines which bound the pie-shaped shutter aperture.Although there are an infinite number of locations for the rectangularpickup about a 360° arc, only four of these locations (located 90°apart) result in a horizontally or vertically disposed picture tubeformat that can be swept evenly by a pie-shaped opening. All otherorientations result in a pickup surface which is skewed unnaturally tothe opening. The undesirability of having a skewed format is evidentwhen one recognizes that the camera (or viewing screen) would alwayshave to be held or shimmed at an angle in order to render horizontalsurfaces horizontal and vertical surfaces vertical.

By constraining the location of the pickup tube relative to the shuttermechanism, the overall physical design of the camera (i.e., the size,shape, and bulkiness) is appreciably affected. Such restraints, as apractical matter, result in a larger, bulkier, less aestheticallypleasing and more cumbersome to operate camera then would otherwiseresult were the camera designer free to place components neatly andcompactly in aesthetically pleasing packages with all controlsconveniently located at the fingertips.

SUMMARY OF THE INVENTION

Accordingly, in order to improve upon prior art shutter mechanisms forvideo cameras, the present invention provides a shutter mechanism whichis capable of operating at vastly increased shutter speeds for sharper,clearer images and for less skewing and distortion. Fast moving objectsmay be studied in slow motion or stop-action with greater clarity.Shutter speeds may be varied over a continuous range, as opposed to indiscrete steps, and the shutter speed may be varied over this continuousrange while the shutter is operating. Hence, with the present invention,it is no longer necessary to stop the shutter while indexing to a newshutter speed. This enables the video camera to automatically respond tomomentary changes in lighting, resulting in a proper exposure at alltimes. In addition, the invention permits the video pickup device to beplaced anywhere in a 360° arc about the rotational axis of the shutter.Hence, design constraints inherent to prior art video cameras areeliminated.

In accordance with the invention, a focal plane shutter for a videocamera is provided comprising a disk mechanism positioned between thelense and pickup tube or device of the video camera for rotation aboutan axis. The video pickup device will be understood to include multipledevices, such as three tube or three device cameras, and other multiple(6, 12, 14, etc.) pickup systems. "Chip" cameras using a plurality (e.g.75,000-300,000) of individual sensors, as well as memory chip andcomputer enhanced cameras are also contemplated as within the scope ofthe invention. Rotation of the disk mechanism about the axis defines anannular locus which is in registration with the pickup and lense. Thedisk mechanism is provided with a single light-admitting apertureintersecting or lying within the locus, whereby the disk mechanism,except for the aperture, is opaque to the passage of light between thelense and the pickup. The invention also comprises a means for rotatingthe disk mechanism. The disk mechanism is disposed in a certain relationrelative to the pickup in order to block light from reaching the pickupat all times, except during a single, uninterrupted interval occurringnot more than once each revolution of the disk mechanism and lasting forless than the period of revolution.

The invention further comprises a focal plane shutter in which the diskmechanism is made up of a first disk disposed between the lense andpickup for rotation about an axis and a second disk disposed between thelense and pickup for rotation about the same axis. Rotation about theaxis defines an annular locus in registration with the pickup and lense.Both first and second disks are provided with an opening in registrationwith or intersecting the annular locus. These openings are registrableby properly adjusting the angular position of one disk in relation tothe other disk to define a light admitting aperture between the lenseand the pickup. A means is provided for rotating the first and seconddisks at a common speed. In addition, means are provided for adjustingthe relative angular positions of the disks relative to one another tothereby adjust the size of the light admitting aperture.

Further, the invention also provides a focal plane shutter for a videocamera having a disk disposed between lense and pickup for rotationabout an axis, the disk having a light admitting opening bounded onfirst and second sides by lines emanating from a point on the diskoffset from the axis of rotation. Preferably, the offset distance isdetermined in accordance with the diagonal dimension of the video pickupsurface.

These and other objects and advantages of the present invention willbecome more apparent from the following description and with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a video camera which employs the shuttermechanism of the present invention;

FIG. 2 is an exploded diagrammatic view illustrating the shuttermechanism of the present invention in conjunction with a lense systemand video pickup;

FIG. 2a is a fragmentary view of the shutter mechanism of FIG. 2;

FIG. 3 is a schematic view of an exemplary video pickup tube in use withthe present invention;

FIG. 4 is a diagrammatic illustration of a raster scan pattern useful inunderstanding the operation of the invention;

FIG. 5 is a diagrammatic illustration of the rectangular raster area ona video pickup face plate, showing the swept illumination thereof as theshutter mechanism rotates;

FIG.6 is a plan view of an alternate shutter disk configuration;

FIG. 7 is a plan view of a first shutter disk in accordance with theinvention;

FIG. 8 is a plan view of a second shutter disk in accordance with theinvention;

FIG. 9 is a perspective view of the disks of FIGS. 7 and 8, in relativeangular position to one another to create a large light admittingaperture;

FIG. 10 is a similar perspective view showing the disks of FIGS. 7 and 8in a different relative angular position to create a relatively narrowlight admitting aperture;

FIG. 11 is a rear elevation view showing a preferred shutter rotatingand adjusting mechanism in accordance with the invention;

FIG. 12 is a cross sectional view of the shutter mechanism shown in FIG.11, taken along line 12--12 of FIG. 11;

FIG. 13 is a cross sectional view of the shutter mechanism shown in FIG.11, taken along line 13--13 of FIG. 11;

FIG. 14 is an exploded perspective view of the primary components of theshutter mechanism of FIGS. 11-13;

FIG. 15 is a fragmentary view of the shutter mechanism illustratinganother embodiment;

FIGS. 16-18 illustrate another embodiment of the invention, particularlyan alternate mechanism for adjusting the shutter disks;

FIG. 19 illustrates another embodiment of the invention particularly ahydraulic system for adjusting the relative angular relationship of theshutter disks;

FIG. 20 is a cross sectional view of the shutter mechanism shown in FIG.19, taken along line 20--20 of FIG. 19;

FIG. 21 is a plan view of a different shutter disk configuration;

FIG. 22 is a diagrammatic view of a shutter disk showing the size, shapeand location of the light admitting opening in greater detail;

FIGS. 23-26 illustrate still another alternate mechanism for adjustingthe shutter disks, with FIG. 24 being a cross-sectional view taken alongline 24--24 of FIG. 23;

FIGS. 27-28 depict a pair of alternate shutter disks with FIG. 28 beinga cross-sectional view taken along line 28--28 in FIG. 27;

FIGS. 29-31 illustrate still another pair of alternate shutter diskswith FIG. 21 being a cross-sectional view taken along line 31--31 inFIG. 30;

FIGS. 32-34 depict a further alternative mechanism for adjusting theshutter disks, with FIG. 32 being an exploded view, FIG. 33 being a viewof the assembled mechanism, and FIG. 34 being a cross-sectional viewtaken along line 34--34 in FIG. 33; and

FIGS. 35 and 36 show a still further balanced shutter disk arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, a video camera in accordance with the presentinvention is illustrated at 20. The camera includes case or housing 22,AC/DC adapter 23, electronic viewfinder 24, viewfinder attachment boom25 and lense 26. The lense 26 is mounted to the front cover 30 of theshutter member 41. The lense 26 has a C-type mount and automatic irisand automatic zoom features operated by a servo motor mechanism 27.Power for operation of the servo mechanism is achieved through cord orwire 28 which is connected to the camera by plug 29. The electronicviewfinder 24, which is adapted to be mounted optionally on the back ofthe camera 20, is connected to the camera by cord or wire 31. The AC/DCadapter 23 converts the incoming AC power source to DC power for use inoperating the various mechanisms of the camera. A bracket or "shoe" 33is positioned on the top of the camera 20 for mounting of variousaccessories, if desired, such as an additional light source. Amicrophone 35 is provided to pick up the audio signals from the subjectbeing video taped. A mounting plate (not shown) or shoulder brace (alsonot shown) are also provided on the bottom of the camera 20 for use inmounting or using the camera.

The shutter member 41 has an adjust knob 43 (or "thumb wheel") whichprotrudes through the edge of the front cover 30 and is used by theoperator to adjust the shutter speed. The adjustment mechanism 32 whichis connected to the knob 43 and which actually adjusts the shutter speedis discussed in detail below. Also, as discussed below, the adjustmentmechanism 32 is all located rearward of the front cover 30 which leavesthe front cover flat and with ample room for manual or automatic zoomlense mechanisms. Since the lenses typically use C-type mounts whichscrew onto the camera, an adapter which would change the focal qualityof the camera would be required if the front cover 30 was not flat.

In the present preferred embodiment of the invention, the camera 20 hasa Sony chassis which has been modified to make it wider and longer. TheSony chassis has a 2/3" SMF Trinicon pickup tube.

FIG. 2 illustrates a few important components of the video camera 20,with exterior housing 22 and most internal components eliminated. Avideo pickup device 36, such as a video pickup tube, is disposed in linewith lense 26 as along the common axis 38 between lense 26 and videopickup 36. Video pickup 36 may be implemented using any of a widevariety of video pickup devices including vidicon tubes, saticon tubes,newvicon tubes, plumbicon tubes, chalnicon tubes, and the like. Also,solid state pickup devices, including optically sensitive random accessmemory devices (RAM), may be used. The invention is also equallyapplicable to systems using multiple pickup devices, such as a threepickup tube system for color video recording. Hence the term "videopickup device 36" will be understood to include such multiple pickupdevices.

Video pickup device 36 has a faceplate 40 onto which the optical imageis projected. The video pickup device 36 converts this optical imageinto a continuous stream of electrical impulses representing the image,and this stream of impulses may be magnetically encoded for storage on amagnetic video tape. While the images are being recorded, the stream ofvideo information may also be fed to electronic view finder 24 or to avideo monitor for an immediate review of the program material as it isbeing recorded.

Also shown in FIG. 2 is the disk shaped rotary focal plane shuttermechanism 42 which is one of the principal components of the shuttermember 41. In the preferred embodiment, shutter mechanism 42 comprises afirst disk member 44 which is positioned adjacent lense 26, and a seconddisk member 46 which is positioned adjacent pickup 36. Shutter mechanism42, including first disk 44 and second disk 46, is positioned betweenlense 26 and pickup 36 and supported for rotation about a central axis48. As shutter mechanism 42 rotates about axis 48 an annular locus 50 isdefined by and remains in registration with faceplate 40 of video pickup36. The same locus 50 is also in registration with the mounting end 52of lense 26. Generally speaking, locus 50 may be considered as theannular portion of shutter mechanism 42 which is illuminated by lightemanating from end 52 of lense 26 or which lies directly adjacentfaceplate 40.

Shutter mechanism 42 is provided with a light admitting aperture 54which lies generally within or intersects locus 50 to permit lightemanating from end 52 of lense 26 to reach faceplate 40 of video pickup36. Except for aperture 54, the remainder of shutter mechanism 42 isopaque to the passage of light.

In a presently preferred embodiment, the light admitting aperture 54 iscomprised of a pair of openings in registration with one another asshown in FIG. 2a. First disk 44 is provided with opening 56 and seconddisk 46 is provided with opening 58. Disks 44 and 46 may be rotatedabout central axis 48 until openings 56 and 58 intersect or overlap todefine the light admitting aperture 54. By altering the angularpositions of the disks 44 and 46 relative to one another, the size oflight admitting aperture 54 can be continuously varied from a thin slit(shown in FIG. 10), through intermediate sized apertures, to a fullsized aperture (shown in FIG. 9) which results when openings 56 and 58are in perfect coincident registration. Preferably openings 56 and 58are the same size and shape.

With reference to FIG. 3, video pickup 36 is shown schematically. Forpurposes of illustrating the invention, video pickup 36 is shown as avidicon tube, however, it will be appreciated that the invention isequally applicable to video camera systems using other types of videopickup devices, including solid state devices. Hence, the invention isnot intended to be limited to any particular type of video pickup. Thevideo pickup device illustrated in FIG. 3 is denoted generally byreference numeral 36, and includes a cylindrical glass tube 60 on whichglass faceplate 40 is secured or integrally formed. Pickup 36 has atarget section 62 comprising a transparent signal electrode 64 depositedon the inside of faceplate 40 and a thin layer of photoconductivematerial 66 which is deposited over electrode 64. The photoconductivematerial has a fairly high resistance when in the dark. Light falling onthe material excites additional electrons into a conducting state,lowering the resistance of the material at the point of illumination.Video pickup 36 also includes an electron gun 68 which may be energizedto produce an electron beam. Horizontal and vertical deflecting coils 70deflect the electron beam in accordance with horizontal and verticaldeflection circuitry 72 to produce a raster scanning pattern on thetarget section 62. A fine mesh screen 74 stretched across tube 60 neartarget section 62 causes the electron scanning beam to decelerateuniformly at all points and approach the target in a perpendicularmanner. The beam is brought to a sharp focus on target section 62 bymeans of longitudinal magnetic fields produced by a focusing coil 76which is energized at the proper focusing voltage by voltage source 78.The video signal output is coupled via output lead 80 to signalamplifying and processing circuitry 82. The signal output on output lead80 constitutes a video signal.

In operation, a positive voltage is applied to one side of thephotoconductive layer 66 by means of the signal electrode 64. On theother side of the photoconductive layer 66 the electron scanning beamdeposits low velocity electrons in accordance with a predeterminedraster scan pattern. A typical raster scan pattern is illustrated inFIG. 4 as it would be viewed from outside faceplate 40. As shown in FIG.4, the raster pattern 84 is generally rectangular, having horizontaldimension 86, vertical dimension 88 and a pair of diagonals 90 and 92which intersect at the raster center point 94. Raster pattern 84 isproduced by successive horizontal sweeps of the electron beam or lines.By convention, these lines are numbered consecutively beginning withline No. 1 at the bottom of raster pattern 84. Scanning starts at thebottom since the image is inverted by the lense. The number of lines mayvary depending upon the resolution of a particular video system. Atypical system might have 525 lines, for example. To minimizeflickering, the raster pattern is frequently generated by interlacingthe odd and even fields. This is accomplished by first scanning all oddnumbered lines (referred to as the odd field), and by then scanning alleven numbered lines (the even field). By convention, both the odd andeven fields commence in the lower right hand corner or origin point 96and end in the upper left hand corner or termination point 98. Eachfield is generated by sweeping back and forth; for example, Line 1 isswept from right to left, Line 3 from left to right, Line 5 from rightto left, etc. When the scanning beam reaches the termination point 98 itis swept diagonally generally along diagonal line 92, to the originpoint 96. This diagonal sweep is called the vertical retrace. During thetime in which vertical retrace occurs, the video signal is blanked bymeans of blanking circuitry 100 (FIG. 3) so that the diagonal retraceline is not visible.

As previously discussed, in the interval between successive scans of aparticular spot on target section 62, any incident light illuminatingthat spot lowers the resistance of the photoconductive layer at thatspot in relation to the light's intensity. Current then flows throughlayer 66 causing the back surface thereof to build up a positive chargeuntil the beam returns to scan the spot. A video output current pulse isgenerated at that spot on signal electrode 64 when the beam restores thepositively charged spot to a zero voltage. As the beam continues toscan, these current pulses are continually emitted to make up the videosignal.

With continued reference to FIG. 3, disks 44 and 46 are axially rotatedby motor 102 which is attached to the back cover plate 45 of shuttermember 41 and protrudes into the housing 22. In the presently preferredembodiment, motor 102 drives disks 44 and 46 at nominally 3600 rpm.Rotation is clockwise as viewed from the motor side, or counterclockwise as viewed from the lense side. Both the disks are oriented sothat openings 56 and 58 are in partial or full registration to definethe light admitting aperture 54 through which light from lense 26 isprojected onto faceplate 40. Motor 102 rotates disks 44 and 46 so thatan image will be projected on faceplate 40 once in each revolution. At arotation of 3600 rpm, 60 separate exposures per second are projected onfaceplate 40. These exposures are timed to occur during the blankinginterval when the scanning beam is executing a vertical retrace. Duringthe remainder of time, faceplate 40 receives no light through the opaquedisks. Hence, the scanning beam always interrogates an unchanging visualimage stored in the photoconductive layer 66 during a vertical retrace.Because the image is unchanging (no new light is admitted to change theimage), the resultant video signal on lead 80 represents a sharp,unblurred video image. Since 60 such individual exposures are made eachsecond, no perceptible flicker is evident when the video signals areviewed on a video monitor.

With reference to FIG. 5, it will be seen that the rotation of disks 44and 46, which cooperate to form shutter mechanism 42, causes faceplate40 to be swept with light once per revolution. As indicated above, it ispresently preferred to illuminate faceplate 40 during the verticalretrace interval of the raster scan cycle. The vertical retrace occursat repeated intervals determined by the electron beam scanning rate andthe number of lines which make up the raster. Thus, in many practicalapplications the illumination of faceplate 40 occurs at intervalscorresponding to the periods between vertical retrace cycles which areelectronically predetermined. By employing a single light admittingaperture 54 the present invention enjoys the highest possible shutterspeed or sweep rate for any given retrace period. To demonstrate this,FIG. 5 may be compared with FIG. 6 which illustrates an alternativeshutter member 104 having two light admitting apertures 106 and 108equally spaced about annular locus 50. Using the shutter mechanism ofFIG. 6, the speed of rotation must be half that of shutter mechanism 42in FIG. 5 in order to illuminate faceplate 40 at the same timeintervals. As indicated, these time intervals are often dictated by andoccur in synchronism with the vertical retrace cycle. Hence, the shutterspeed, or the speed at which light is swept across faceplate 40, of thetwo-aperture embodiment of FIG. 6 is one-half that of thesingle-aperture embodiment of FIG. 5. A practical effect is that thesingle-aperture embodiment illuminates faceplate 40 for half as long asthe two aperture embodiment for each illumination interval. Thesingle-aperture embodiment is thus capable of capturing sharp images offast moving objects which appear as a blur through the two-apertureembodiment.

Preferably disks 44 and 46 are thin circular disks of aluminum ortitanium which are supported for rotation about their respectivegeometric centers. In order to place the inertial centers of the disksat their geometric centers, the disks are provided with counterbalancingcutout regions. These counterbalancing cutouts cause each disk's centerof mass to coincide with its geometric center. Hence, when the disks arespun, the polar moment of inertia is zero or substantially zero. FIG. 7illustrates disk 44 which is provided with cutout region 110; and FIG. 8illustrates disk 46 which is provided with cutout regions 112. Cutoutregion 110 on disk 44 is disposed at an average distance 148 from thegeometric center 114 that is different from the average distance 150 atwhich cutout regions 112 are disposed on disk 46. Thus, when disks 44and 46 are spun about central axis 48 through their common geometriccenters 114, cutouts 110 and 112 nowhere overlap. Thus, shuttermechanism 42, comprising disks 44 and 46 remains opaque to the passageof light (except at the aperture 54), notwithstanding the fact that bothindividual disks 44 and 46 are provided with cutouts. FIGS. 9 and 10illustrate disks 44 and 46 in overlapping disposition exemplary of twopossible aperture sizes. In both Figures, note that cutouts 110 and 112nowhere overlap. Further in this regard, since both disks 44 and 46 arerotated as a common unit or in phase with one another, the cutouts 110and 112 do not in normal operation overlap with openings 56 and 58.

FIGS. 27 and 28 illustrate another pair of shutter disks 42' and 44'which can be used in accordance with the present invention. The diskshave central mounting apertures 45' and 47' and single light admittingapertures 56' and 58'. The disks 42' and 44' are mounted, rotated andoperated in a manner similar to that described above with references toFIGS. 5 and 7-10, or alternatively as described below with reference toFIGS. 32-34.

The disks 42' and 44' are counterbalanced to reduce their polar momentsof inertia. Disk 42' has recessed relief area 43' removed from one ofthe surfaces of the disk while disk 44' similarly has recessed reliefarea 49' removed from one of its surfaces. The relief areas 43' and 49'correspond in weight and volume to the apertures 56 and 58' respectivelyand are positioned on the opposite side of the center of the disk fromthe apertures in order to create a balanced disk for rotation. Unlikethe counterbalancing cutout areas described above with reference toFIGS. 7 and 8, however, the relief areas 43' and 49' do not extendentirely through the disks. Instead, the relief areas are machined onlypart way into one surface of each disk forming a recess. The machiningcan be carried out by any known process, such as by milling,electrochemically machining, electrical discharge machining (EDM),photochemical machining, or the like. The forming of a recess ratherthan an aperture provides the necessary counterbalancing and also leavesthe disks 42' and 44' opaque to light, except for the light admittingapertures 56' and 58'.

If the recessed relief areas 43' and 49' are sufficiently large (inorder to balance large-sized light admitting apertures), it may benecessary to provide stiffening ribs 500 in the recessed areas. Theshutter disks 42' and 44' are relatively thin and large-sized reliefareas might weaken the disks and allow them to warp or fail duringrotation and use.

When the disks 42' and 44' are used in the shutter mechanism, therecessed relief areas are positioned adjacent to and facing one another.In this manner, the side 51' facing the video pickup device presents asmooth interrupted surface (except for the light admitting aperture58'). The presence of a cutout opening or relief area facing the videopickup device could cause extra lines in the video picture; the changein capacitance between the surfaces might affect the electrons on thesurface of the video pickup device which might create lines on the videooutput, or the video pickup device might erroneously sense the edges ofthe cutout or relief area and also create unnecessary lines on theresultant video display.

It also might be significant to present a smooth interrupted surfacefacing the shutter system timing mechanism (sensor 250 and controlcircuitry 252) to eliminate the possibility that the sensor and timingmechanism might provide a false reading corresponding to the position ofthe counterbalancing opening rather than the light admitting aperture.

Another pair of shutter disks 502 and 504 are shown in FIGS. 29-31. Thispair of disks can be used with the shutter adjustment mechanism shown inFIGS. 32-34 (described below). For this purpose (as explained in moredetail below), shutter disk 502 has a small center opening 503 and apair of curved retention and adjustment slots 506, while disk 504 has arelatively larger center opening 505 and a small locating hole 508. Theslots 506 allow for minor adjustment of the shutter disks to align thelight-admitting apertures during final assembly.

Disk 502 has a light-admitting aperture 510 and a correspondingcounterbalancing cutout region 512. The aperture 510 is significantlylarger than the apertures 56' and 58' in FIG. 27 so that slower shutterspeeds can be obtained. Similarly, disks 504 has a light-admittingaperture 514 which is the same size and shape as the aperture 510 ondisk 502 so that the two disks when placed together cooperate to form asingle light-admitting aperture for the video camera. With the shuttermechanism shown in FIGS. 29-31, a wide range of shutter speeds from1/250 of a second to 1/20,000 of a second can be obtained. This alsoallows the video camera to be used in low light level conditions, suchas at indoor sporting events.

Disk 504 has a counterbalancing recessed relief area 516 formed in oneside. The relief area 516 is preferably formed by one of the variousmetal removal procedures mentioned above and is sufficiently large inorder to counterbalance the large opening 514. Stiffening ribs 500provide structural support for the relief area 516 and prevent the diskfrom warping or failing during use.

Apertures 510 and 514, as well as cutout area 512, preferably are formedinside the perimeter of the disks 502 and 504 leaving rim edges 520. Ifdesired for space considerations inside the camera, the rim edges 520could be eliminated and the cutout areas extended to the edge of thedisks. It is preferred, however, to retain the rim edges 520 in order toreduce noise inside the shutter mechanism.

As shown in FIGS. 29 and 30, the two shutter disks 502 and 504 havedifferent types of counterbalancing areas (cutout aperture 512 andrecessed relief area 516, respectively). This is due to the fact thatthe cutout areas (such as 512) are easier to form and machine than therecessed relief areas (such as 516) and that only the surface of theshutter mechanism adjacent the video pickup device needs to be flat anduninterrupted.

Another manner of counterbalancing the shutter disks in order to placethe inertial centers of the disks at their geometric centers and toeliminate the polar moments of inertia is shown in FIGS. 35 and 36. Theshutter disk 700 has a portion of another disk 702 secured to it to actas a weight to counterbalance the amount of material taken out of disk700 when the light admitting aperture 704 is formed.

The disk portion 702 has a corresponding aperture 706 which is identicalin size and shape to the aperture 704 in disk 700. The disk portion 702is glued or laminated to disk 700 with the two apertures 704 and 706 inalignment. A type of glue which can be used to hold the disk portion 702to disk 700 is Scotch-Weld CA-8 by the 3M Company.

As indicated earlier, the disk 700 is preferably made of aluminum. Inorder to provide a disk portion 702 which is relatively thin so that itwill not affect the operation of the shutter disk mechanism, the metalfor the disk portion 702 preferably is heavier. With the disks shown inFIGS. 35 and 36, a disk portion 702 made of brass and 0.006 inches inthickness can be used to balance a disk 700 made of aluminum and 0.015inches in thickness.

Although only one shutter disk 700 is shown in FIGS. 35 and 36, it is tobe understood that one or two similar shutter disks can be utilized in ashutter disk mechanism in accordance with the present invention.

Unlike the situation with prior art focal plane shutters, the focalplane shutter of the present invention permits the operator tocontinuously vary the shutter speed while the shutter is in motion.Although the shutter mechanism 42 rotates at a constant speed insynchronism with the raster scan pattern, the relative size of aperture54 may be continuously varied by a number of different mechanisms toalter the shutter speed. In this regard, the shutter speed will beunderstood as a measure of the length of time during which the image isprojected on a given point on faceplate 40 during a given revolution ofshutter mechanism 42. In general, the larger the relative size ofaperture 54, the longer an image is projected on faceplate 40, and hencethe slower the shutter speed. Hence, FIG. 9 depicts the largest sizeaperture 54 corresponding to the slowest shutter speed; while FIG. 10depicts a relatively narrow or small aperture 54 corresponding to one ofthe fastest shutter speeds. In practice, utilizing disks 44 and 46having the size and shape shown in FIGS. 7 and 8, at a rotational speedof 3600 rpm, the invention will provide continuously variable shutterspeeds from nominally 1/500 to 1/20,000 second. The 1/20,000 secondspeed is achieved with an opening subtending a 1° arc.

A number of mechanisms may be alternatively used to change the relativeangular position of one disk with respect to the other and to therebychange the effective size of aperture 54. These mechanisms includemechanical linkages as well as hydraulic actuators. Alternatively, disks44 and 46 might also be rotated using separate phase-locked motorswherein at least one of the motors is driven by a source capable ofintroducing a phase lag or lead to thereby alter the relative angularposition of the disks to one another.

One preferred mechanism for mounting and operating the shutter mechanism42 is illustrated in FIGS. 11-14. The shutter member 41 comprises athin, relatively square shaped housing 47 which is adapted to be mountedby screws or bolts through openings 116 to the front of the case orhousing 22 of the video camera 20. The housing 47 is made of aluminum oranother material which has similar strength and weight characteristics,and which can be machined and formed in the shape and configurationsshown. The interior of the housing has one or more bores or recesses init, as described below, and the hollow interior is covered by back cover45. The back cover 45 is neatly positioned in recess 115 in the housingand held in place by a series of small screws 117.

The lense 26 is mounted on the front 30 of the housing 47. A stainlesssteel threaded lens ring 118 is pressfit in opening or bore 119 in thehousing and the end 52 of the lense 26 is threaded securely into it. Thevideo pickup 36 is positioned adjacent the back cover 45 of the housingon the same axis 38 as the lense. Typically, the video pickup isadjustable axially in the camera 20 for focusing. The distance D betweenthe faceplate 40 of the video pickup 36 and the end 52 of the lense 26is between 0.400 and 0.500 inches and has to be maintained in this rangefor proper focusing and operation of the camera without additionaladaptors and the like. If desired, the video pickup 36 can be attachedto the housing 47 as shown in FIG. 12. A threaded annular-shaped ring120 is secured, for example by screws 121, into recess 122 in the backcover 45 and mates with threaded ring 123 on the video pickup 36. Inthis manner, the video pickup can be axially adjusted precisely andaccurately.

A filter wheel 124 is interposed between the lense 26 and video pickup36. The wheel 124 has three filters 126 of various colors commonly usedin videotaping. The wheel 124 rotates on bushing 128 which is secured tothe housing 47 by screw 129. A portion of the wheel 124 protrudesoutside the housing 47 (as shown in FIG. 11) so that it can be manuallyrotated. For this purpose, the outside perimeter 125 of the wheel 124 isknurled or ribbed. When the wheel 124 is rotated, one of the filters 126becomes aligned axially with the lense 26, video pickup 36 and lightadmitting aperture 54 in the shutter disks 44 and 46. In this manner thelight entering the video pickup from the lense is filtered as desired.An indexing ball bearing 130 is set in a recess 131 in the housing 47and mates with one of four shallow recesses 132 in the filter wheel 124.The ball bearing and mating recesses act to index the filter wheel toone of four positions, three of which interpose a filter 126 in thecamera light path and the fourth of which prohibits any light fromentering the camera. The latter position of the filter wheel is used toprotect the expensive video pickup 36 during storage and handling of thecamera, or when the camera might be exposed to undesirable bright light.

As shown in FIG. 12, the filter wheel 124 is contained in a recess 134in the interior of the housing 47 and is also positioned between thedisks 44, 46 and the lense 26. It is also possible to arrange the partsso that the filter wheel is positioned between the disks 44, 46 and thevideo pickup 36. In either situation, the filter wheel will perform thesame function and be manually operated from outside the housing. Thefinal positioning of the filter wheel is determined by the dimension Dand by whether a mechanism is needed, such as ring 120, to hold and/oradjust the end of the video pickup 36.

A separate cover 136 is utilized to cover the filter wheel in thehousing 47. One edge 137 of the cover 136 is curved to match and matewith the edge of the circular back cover 45. Several screws 138 hold thecover 136 to the housing 47.

Disks 44 and 46 are provided with central openings 152 and 154,respectively, for mounting on a hub member 156. Hub member 156 isdisposed within or slightly below motor support housing 158 which inturn is secured to back cover 45 of housing 47. The support housing hasa flange 159 which is positioned in mating recess 160 in cover 45. Thehousing 158 is secured to the cover 45 by a number of screws 161. Motor102 is fastened to motor support housing 158 and is coupled to hubmember 156 for imparting rotary motion thereto. Disks 44 and 46 arefastened to hub 156 and rotate therewith. Central openings 152 and 154are each provided with a pair of tangentially extending slotted openings162-165. More specifically, central opening 152 is provided with a firstslotted opening 162 extending tangentially or spirally outwardly fromgeometric center 114, and a second slotted opening 163 extendingtangentially or spirally in a diametrically opposite direction toslotted opening 162. Similarly, central opening 154 is provided with afirst slotted opening 164 and a second diametrically opposing slottedopening 165. (For ease of reference, see FIGS. 7 and 8, as well as FIG.14). When disks 44 and 46 are positioned in registration with oneanother on hub 156, the slotted openings 162-165 cross one another todefine a pair of V-shaped or X-shaped configurations as shown in FIGS. 9and 10. As explained more fully below, the precise configurationsdefined by the slotted openings determines the degree to which openings56 and 58 overlap, thereby defining the size of light admitting aperture54.

In order to change the configuration of the slotted openings 162 through165, pins 167 and 168 are slideably secured within hub 156 for radialmovement inwardly and outwardly with respect to hub axis 48. Hub 156 isprovided with a central opening 170. Hub member 156 is further providedwith an axial slot 175 for slideably receiving an arrowhead-shaped bladeactuator 174 disposed on shaft 172. Shaft 172 is pressfitted orotherwise securely fastened at one end to drive shaft 173 of motor 102.Shaft 172 is fastened at its other end to the blade actuator 174 bybeing slip fitted inside cylindrical housing 176 which is secured to theblade. Shaft 172 has a slotted end 177 which slips over the blade. Theactuator blade 174 is inserted into slot 175 and rests against the pins167 and 168.

Throw-out bearing mechanism 180 is securely fastened over shaft 172 andis coupled to a rocker arm or lever 181. Lever 181 is supported atfulcrum point 183 for rocking movement which causes the arrowhead-shapedblade actuator 174 to be translated along axis 48. Lever 181 has a yoke182 and is pivotably attached to bearing 180 by pins 185.

The inner ends of pins 167 and 168 bear against edges 184 and 186 ofblade 174 and radially translate inwardly and outwardly to follow edges184 and 186 as the actuator blade is moved axially in slot 175. Theouter ends of pins 167 and 168 bear against disks 44 and 46 at shoulders188 and 190. Specifically, shoulders 188 and 190 bear against portionsof disks 44 and 46 which define the perimeters of slotted openings162--165 (as best shown in FIGS. 9 and 10). Thus, radial movement ofpins 167 and 168 is translated into rotational movement of disks 44 and46 in opposite directions to one another.

A pair of springs 192 and 194, disposed in arcuate-shaped slots 196 and198 in disks 44 and 46, bias disks 44 and 46 to rotate in directionsopposing the outward movement of the pins 167 and 168. (For ease ofreference the spring slots in disks 44 and 46 have both been marked withthe same reference numbers 196 and 198; curved slots 196 and 198 areidentical in both disks.) The relationship of the springs to the disksis best shown in FIGS. 9, 10, 12 and 14. One end of each spring 192, 194is hooked in a hole in one disk 44, 46 and the other end of each springis hooked in a hole in the other disk. For example, spring 192 has oneend 193 fastened in hole 193' in disk 44 and the other end 195 fastenedin hole 195' in disk 46. Similarly, spring 194 has one end 197 fastenedin hole 194' in disk 44 and the other end 199 fastened in hole 199' indisk 46.

When the springs 192 and 194 are at "rest" (in their untensionedposition), the openings 56 and 58 completely overlap (FIG. 9). At thisposition, the blade actuator 174 applies no force on pins 167 and 168.When the shutter speed is increased (i.e., the light admitting apertureis made smaller) and the blade 174 is pushed axially downwardly into hub156, and pins 167 and 168 are pushed outwardly into the "Vs" between thecentral openings of the disks. At this position (as illustrated in FIG.10), the springs 192 and 194 are extended and the force caused by thepins 167 and 168 overcomes the force of the springs. Later, when theshutter speed is decreased and the aperture 54 is enlarged, the actuatorblade 174 is retracted and the force of the springs 192, 194 pushes thepins radially inwardly and tries to restore the disks to their "rest"position.

The axial movement of the arrowhead-shaped blade 174 and thus theresultant opening and closing of the light admitting aperture 54 iseffectuated by movement of the lever 181. As indicated above, the lever181 is pivoted at fulcrum point 183 and one end is connected with a yoke182 to thrust bearing 180 and directly moves the blade actuator 174. Theother or distal end 202 of the lever 181 is fitted into a slotted cap204 containing a nylon mover 206 rotatably secured therein. The cap 204is secured to back cover 45 with screws 205.

The lever 181 protrudes through a slot 208 in the motor support housing158 and passes directly through a cap housing 210. The lever arm ispositioned in a rotatably mounted bushing 212 in the cap housing 210.The cap housing 210 is secured to the back cover 45 by screw 214.

Mover 206 has a beveled or angled surface 216 upon which distal end 202rides. Mover 206 is fastened to and a part of adjustment knob 43 whichwas previously described. The knob 43 rotates on a peg 218 in recess 219of housing 47 and has a knurled or ribbed edge 220 for manual rotation.Cover member 221 is positioned over the mover and adjustment knob andholds the knob in place on peg 218. The cover member 221 also acts asthe seat for slotted cap 204.

Adjustment of the shutter aperture 54 is controlled by the cameraoperator by manual rotation of the knob 43. As indicated earlier, theadjustment of the shutter aperture can be carried out while the disks44, 46 are rotating; the relative angular positions of the disks can beadjusted while they are rotating in a common direction about their axisof rotation. It is also possible for the shutter aperture to be adjustedautomatically, for example by means of a motorized system or linkagewhich is activated electronically by the outgoing video level.

As best shown by FIGS. 12-14, the disks 44 and 46 are positioned on thehub 156 and situated for rotation in a recess 135 in the interior ofhousing 47. The disks 44 and 46 are positioned next to each other onflange 222 and rest against larger flange 224. The disks are held on thehub by washer 226 and bearing 228. The bearing 228 is seated in bore 230in housing 47 and the hub is seated firmly in the bearing. Therelationship of the bearing 228, washer 226, disks 44 and 46, and flange224 hold the disks securely in position in the housing and on the hub,and yet allow them to rotate freely with the hub 156.

In operation, when the motor 102 is activated through appropriatecircuitry and controls 103 by the camera operator, the drive shaft 173with cylindrical shaft 172 attached thereto rotates the arrowhead-shapedblade actuator 174 which in turn rotates the hub 156 and the disks 44and 46. As indicated earlier, blade 174 is positioned in axial slot 175in hub 156.

Another arrangement for mounting the hub 156 for rotation in the shuttermember 41 is shown in FIG. 15. The hub 156 is situated for rotation inbearing 240 which in turn is seated in recess 242 in back cover 45.Bearing 240 at the upper end of the hub as shown in FIG. 15 replaces thebearing 228 at the forward end of the hub in the embodiment shown inFIGS. 12-14. Together with bearing 240, however, it is also possible touse, although it is not necessary, self-centering pivot bearing 244. Ifutilized, bearing 244 is positioned in recess 246 in housing 47 andholds conical end 248 of hub 156.

To aid in the timing of the shutter system, sensor 250 and controlcircuitry 252 are provided. The sensor is positioned in opening 254 inback cover 45 and is set up to "read" painted dot 256 on disk 46. Thedot 256 is positioned at a prespecified and angular location fromopening 58 on disk 46 (and hence from light admitting aperture 54). Inthe embodiment shown, the sensor 250 is positioned 180° from theopening. The sensor senses the dot each revolution of the disk and,through the control circuitry 252, insures that the video camera systemis in the correct mode of operation when the disk openings 56 and 58 arein axial alignment with the video pickup 36. This arrangementcompensates for any fluctuations in the speed of the motor 102, anyphase-lock losses which might be encountered during adjustment of theshutter aperture, or any other changes or variations in the system whichmight affect the proper timing and orientation of the aperture 54 withrespect to the positions of the lense and video pickup.

An alternate mechanism for adjusting the shutter aperture and therelative angular rotation of the rotating disks relative to one anotheris shown in FIGS. 16, 17 and 18. This embodiment differs from thatdescribed above relative to FIGS. 11-14 in the arrowhead-shaped actuatorblade, the structure used to transmit the movement of the blade to therelative angular positions of the disks, the center openings of thedisks, and changes in the hub to incorporate these differences.

The disks 300 and 302 are shown in their operating stacked relationshipin FIG. 16. Each of the disks has a similar sized opening 304, 306 whichtogether act as the light admitting aperture 308 in the same manner thatopenings 56, 58 in disks 44 and 46 form aperture 54 discussed earlier.The disks 300, 302 also have balance openings 310 and 312 which aresimilar in size, shape and function to the openings 110 and 112 in disks44 and 46. The center openings 314 and 316 of the disks 300, 302 arecircular and are adapted to fit on and be turned by hub 318.

The actuator blade 320 is not as thin as blade 174 discussed above andadjusts the relative angular relationship of the disks in a differentmanner, but the general purpose of the blade 320 is the same. The blade320 is attached to a motor driveshaft 322 for rotation, fits inside androtates the hub 318, and is adapted to move axially along axis 48 toadjust the size of the aperture 308. Brackets 330 and 332 are slidinglysecured in channels 334, 335, 336 and 337 in blade 320 and protrude andmove radially outwardly from the hub 318 in passageways 340 and 341.Pegs 343 and 344 extend from brackets 330 and 332 and fit into slantedopenings 346, 347, 348 and 349 in the disks 300 and 302. Openings 346and 349 are in disk 300 and openings 347 and 348 are in disk 302. Theseopenings are arranged in pairs which overlap at a certain point and pegs343 and 344 extend through them.

As the actuator blade 320 is moved axially along axis 48, the bracketsand pegs move radially and slide within the slanted openings. As thepegs are forced radially outwardly, the slanted openings tend to crosswhich causes the disks 300, 302 to rotate relative to one another andthereby close the aperture 308. The process is repeated in the oppositedirection for the aperture to be widened. The embodiment of FIGS. 16-18does not utilize springs in the operation of the adjustment mechanismfor the aperture and less possible loading of the motor 102 shouldresult.

Other mechanisms for moving the actuator blade 174 axially in the slot175 can also be utilized. For example, in place of theknob-mover-lever-yoke mechanism shown and described relative to FIGS.11-14, it is also possible to provide a slotted ring attached to a slidemechanism for axial movement of the actuator blade. Such an alternatemechanism is shown in FIGS. 23-26.

The ring 281 has three elongated slots 283 positioned equidistantlyaround its circumference. The slots are angled approximately 30° fromthe horizontal (as illustrated by angle 285 in FIG. 25). The thrustbearing 287 is similar to thrust bearing 180 described earlier, but hasthree pegs 289 extending outwardly from it. The pegs 289 are positionedequidistantly around the circumference of the bearing and are slidinglypositioned in the slots 283. The thrust bearing is secured to shaft 172inside motor support housing 158. Lever 291 is attached to the outsideof the ring 281 and extends through a slot 293 in housing 158. The leveris connected to a slide mechanism (not shown) on the exterior of theshutter mechanism housing 47, preferably along an edge thereof. Movementof the slide mechanism causes a corresponding rotation of the ring 281around central axis 48. Rotation of the ring 281 due to the angled slots283 in turn causes a direct axial movement of the actuator blade 174along axis 48.

Another preferred embodiment for rotating the shutter disks andcontinuously adjusting the shutter speed of a video tape camera is shownin FIGS. 32-34. This embodiment utilizes a pair of shutter disks similarto those shown in FIGS. 29 and 30, although it is understood that manyof the aforedescribed shutter disks could be utilized instead, so longas they are adapted to mount on the hub members of FIGS. 32-34.

The disks 502 and 504 are rotated by motor 102. Disk 502 is mounted oninner hub member 530. Screws 532 positioned through slots 506 secure thedisk 502 to the hub member. The screws are positioned in threadedopenings 534 in the flange 536 of the inner hub member 530. The centralopening 503 in disk 502 is positioned over cylindrical member 538.

Disk 504 is positioned on outer hub member 540. Opening 505 in disk 504is positioned over cylindrical member 542 on hub member 540 and keyed inposition for rotation therewith by means of pin 544 which is positionedin opening 508. Inner hub member 530 is positioned within outer hubmember 540 and the hub members are adapted to be adjustably rotated inopposite directions relative to one another. When the two hub membersare coupled together, the disk 502 is positioned directly adjacent disk504 and holds disk 504 in place. When the two hub members are adjustablyrotated relative to one another, the light admitting aperture of theshutter disk mechanism and the shutter speed is adjusted accordingly (inthe same manner as explained above).

The hub member 540 is positioned in opening 546 in the back cover member548. Hub member 540 is held in place on the cover member 548 by maincarrier bearing 550 which is positioned over cylindrical flange 552 onthe hub member 540 and secured in place by lock ring 554. Housing 556 ispositioned over the carrier bearing 550 and secured to the back covermember 548 by a plurality of screws 557. In order to facilitate accessto the screws 557, the widest flange 558 on outer hub member 540 has acorresponding number of notches 559. Openings 560 in the cover member548 allows the screws 557 to be secured in threaded holes 562 in thehousing 556.

Housing 556 has three axial-oriented elongated slots 564 spaced 120°apart around its circumference. Dowel pins 566 on control ring 568 fitwithin the slots 564 and allow the control ring to move axially alongcentral axis 570 of the adjustment mechanism without any rotation.

Motor 102 is mounted on the end 572 of housing 556. Screws or smallbolts (not shown) pass through openings (not shown) in the hollow centerof the housing 556 and are secured in threaded holes 574 on the motor102. The motor 102 has a drive shaft 173 and a spindle drive member 576.The spindle drive member 576 has a slot 578 in it which is used torotate the inner and outer hub members (530 and 540) in a manner to bedescribed below and thus in turn rotate the disks 502 and 504.

Tubular member 580 is one of the key elements used to both help rotatethe disks 502 and 504 and at the same time assist in the adjustment ofthe shutter opening. The tubular member is a small piece of brass tubingwhich has a smaller-diameter portion 582 at one end and two pairs ofangled slots 584--584 and 586--586 formed in it. The end portion 582fits within bearing 588 which is seated in the control ring 568. Thetubular member 580 is held in place in the bearing 588 and control ring568 by snap ring 590. Snap ring 590 fits within groove 592 on the endportion 582 after it is slipped through the bearing 588. The bearing 588is securely held in place in the control ring 568 by a plurality ofscrews 594.

The tubular member 580 is movably connected inside the inner and outerhub members by dowel pins 596 and 598. Pin 596 fits through a pair ofopposed holes 600 in hollow inner hub member 530 and also through thepair of slots 586--586 in the tubular member. A pair of notches 602 inthe outer hub member allow access to the holes 600. Pin 598 fits througha pair of holes 604 in the hollow outer hub member, a pair of slots 606in the inner hub member, and the pair of slots 584--584 in the tubularmember 580.

The two pairs of slots 584--584 and 586--586 are situated at angles tothe central axis 570 of the adjustment mechanism (and thus the axis ofthe tubular member 580) as well as to one another. Preferably each pairof slots is oriented about 55° from the axis of the tubular member 580and thus 110° from the other pair of slots. In this manner, when thetubular member is connected to the two hub members by the dowel pins, anaxial movement of the tubular member will cause relative rotation of thetwo hub members in directions opposite to one another. This in turn willadjust the light admitting shutter aperture.

The slot 578 in the spindle drive member 576 also mates with one of thedowel pins 596 or 598 when the adjustment mechanism is assembledtogether (FIGS. 33-34). In this manner, the motor 102 directly drivesthe shutter disks 502 and 504 (at approximately 3600 rpm). The motorrotates the tubular member 580 which in turn through the dowel pinconnections rotates the inner and outer hub members, which in turnrotate the attached shutter disks.

The adjustment of the light admitting aperture is controlled by a slide,lever, thumb wheel, or the like on the external surface or edge of theshutter mechanism. (In the manner described earlier). The lever or slideis attached to control arm 610 which is press fit on the end 611 ofcontrol sleeve 612. The lever, slide or the like is connected to theattachment hole 613 and slot 614. Alternately, the control arm andcontrol sleeve could be formed in one piece (for example made ofinjection molded plastic).

The control arm 610 and control sleeve 612 are positioned over one end572 of the housing member 556 and rest against a shoulder 563. A washer616 can be positioned between the control arm 610 and the shoulder 563to aid movement of the arm and sleeve relative to the housing.

The control sleeve 612 has three elongated slots 618 spacedequidistantly around its circumference (120° apart). The slots 618 areangled relative to the axis 510 of the adjustment mechanism. The slots618 cooperate with the axial-aligned slots 564 in the housing member 556such that when the control sleeve 612 is positioned on the housingmember, the dowel pins 566 of the control ring 568 protrude through bothsets of slots (564 and 618). In this manner when the control arm andcontrol sleeve are rotated by the external slide, lever, etc., thecontrol ring is caused to be displaced axially (along axis 570) which inturn, as explained above, causes a similar axial movement of the tubularmember 580, a relative rotation of the inner and outer hub members 530and 540, and a corresponding change in the shutter opening on the disks502 and 504.

A plastic sleeve 620 is slipped over the control sleeve when themechanism is assembled and protects the internal parts of the mechanismfrom dust and other debris. The sleeve-dustcover 620 is preferably madeof polycarbonate and is sized to fit snugly over the control sleeve sothat it will not be displaced during use of the camera. A washer 622 isalso provided to seat between the control sleeve 612 and the motor 102.

The parts of the adjustment mechanism should be made of any materialswhich will allow the parts to perform their necessary functions.Preferably, the parts are made of common materials such as aluminum(shutter disks, housing member, control ring, control sleeve), stainlesssteel (inner hubmember, outer hubmember), brass (tubular member, controlarm, spindle drive), phenolic resin (back cover) and plastic (sleevedustcover). The various washers, screws, dowel pins and bearings can bemade of any standard metal materials.

Still another embodiment for continuously adjusting the shutter apertureis illustrated in FIGS. 19 and 20. In this embodiment, a hydraulicmechanism is utilized which consists essentially of a master cylinderand double piston arrangement. The master cylinder comprises a smallpiston 360 slidably positioned in cylindrical bore 362 in housing 363.The piston 360 has a seal 364 thereon which sealingly engages the wallsof the cylinder 362. A piston rod 366 is pivotably attached at one end368 to the piston 360 and is pivotably attached at the other end 370 byscrew 371 to an adjustment knob 372. The knob 372 has a knurled orribbed edge 374 for manual rotation and is rotatably situated on pivotpeg 376.

A pair of pistons 380 and 382 are slidingly positioned in cylindricalbore 384 in hub 386. The pistons have seals 392 and 394 on their innerends for sealingly engaging the walls of the cylinder 384. A screw 396prevents the pistons 380 and 382 from touching or sliding past thecenter point in the cylinder, and also provides a port for "bleeding"the hydraulic system. The pistons have rounded outer ends 398 and 400which mate with the "X" or "V"-shaped configurations of the disks 388and 390. The "X" or "V"-shaped configurations are not shown in FIGS. 19and 20, but they are the same as the ones described earlier relative toFIGS. 9 and 10. In this regard, the ends 398 and 400 of the pistonsperform the same function and operate in a similar manner as theradially extended pins 167 and 168.

The hydraulic path between cylinders 362 and 384 includes passageway 402and recess 404 in housing 363, and passageway 406 in hub 386. All of theportions of the hydraulic path are filled with an appropriate hydraulicfluid. A seal 408 seals the joint between the hub 386 and the walls 405of the recess 404. The seal 408 preferably is a spring seal with a smallspring 409 embedded in it and utilized to insure sufficient sealingqualities to the seal. The end 410 of hub 386 is rotationally positionedin the seal 408 and the hub is rotated by a motor (not shown). The driveshaft of the motor is mechanically connected to slot 412 on the top ofhub 386 and rotates it directly. The remaining features of the shuttermechanism shown in FIGS. 19 and 20 are the same as or the equivalent tothose described earlier.

In operation, the shutter aperture is adjusted by manual rotation of theknob 372. Rotation of the knob 372 slides the piston 360 axially in itscylinder and causes the hydraulic fluid in the system to actuate thepistons 380 and 382 in the hub. Activation of the pistons 380 and 382radially outwardly causes the ends 398 and 400 to be pushed or forcedinto the "X" or "V"-shaped configurations on the disks and therebyrotate the disks in opposite directions and close the light admittingaperture. When the aperture is desired to be made larger (and thus theshutter speed is desired to be slowed down), the knob 372 is rotated inthe opposite direction. This slides the piston 360 toward the knob andin turn "pulls" the pistons 380 and 382 toward each other in cylinder384 in the hub. Springs on the disks, such springs being similar tothose described above relative to FIGS. 9 and 10, act to rotate thedisks back toward their open-aperture position.

While a presently preferred embodiment employs a single light admittinglight aperture 54 for maximum shutter speed at a given exposure rate,the various mechanisms described above for continuously adjusting theshutter speed while the shutter is in motion are not limited to thesingle aperture embodiment. In general, the shutter speed adjustmentmechanisms of the present invention are equally useful with multipleaperture shutters, such as the two-aperture shutter of FIG. 6.Furthermore, while the presently preferred aperture is of a particularshape and location, yet to be discussed, the shutter speed adjustmentmechanisms are equally useable with other aperture shapes and locationssuch as the pie-shaped apertures 450 and 452 on disk mechanism 454, asillustrated in FIG. 21. As is apparent from FIG. 21, the side surfaces460, 462, 464 and 466 of the two openings 450 and 452 fall along radiansfrom the center 468 of the disk mechanism 454. Furthermore, theinventive concept of utilizing a single-aperture for maximized shutterspeed may be exploited with shutters having shapes and locationsdiffering from the presently preferred shape and location shown in FIGS.7, 8 and 22 and more fully explained below.

With reference to FIG. 22, the presently preferred apertureconfiguration will now be discussed. In order to provide uniformillumination across faceplate 40, the aperture defining openings 56 and58 of disks 44 and 46, respectively, are formed with the unique shapeshown in FIG. 22 at the location shown. (The same shaped openings arealso shown in FIGS. 5-10.) Preferably openings 56 and 58 are identical,hence only opening 56 will be discussed herein. Opening 56 is bounded ona first side 470 by line 472 and bounded on a second side 474 by line476. Lines 472 and 476 both emanate from a point 478 on the surface ofdisk 44. Point 478 is offset at a predetermined distance 480 from thegeometric center 114 of the disk. (It will be recalled that the centralaxis of rotation 48 of the disks is through the geometric center 114).Opening 56 is further bounded on third and fourth sides 482 and 484 bythe concentric inner and outer boundaries of annular locus 50. Lines 472and 476 define an acute angle 486.

In the presently preferred embodiment, the general size of opening 56 islargely determined by the size of faceplate 40, and more particularlydetermined by the size of the rectangular area 488 swept by the electronbeam during the raster scan. For convenience, rectangular area 488 willbe further described using the reference numerals used to describe theraster 84 of FIG. 4, where applicable. Point 478 is positioned at thepredetermined distance 480 from geometric center 114 such that a line400 bisecting angle 486 will coincide with one of the diagonals ofrectangular area 488. In FIG. 22, the bisecting line 490 overliesdiagonal line 92. Angle 486 is constructed so that lines 472 and 476 areroughly tangent to the circumference of pickup 40 when disk 44 isrotated to the position where bisecting line 490 and diagonal line 92coincide.

The predetermined distance 480 is preferably equal in length to eitherof the diagonal lines 90 or 92 of the raster 84. The precise location ofpoint 478 may be constructed by scribing an imaginary rectangle 494 onthe surface of disk 44, the imaginary rectangle being the exact size andshape of rectangular area 488. The imaginary rectangle 494 touchesgeometric center 114 at corner 496 and is rotationally oriented 90degrees with respect to rectangular area 488. Point 478 is located atthe corner of imaginary rectangle 494 diagonally opposite corner 496.

By constructing openings 56 and 58 in accordance with the above, a moreeven exposure is obtained. The resulting aperture configuration allowsmore light to reach faceplate 40 for a given shutter speed or exposureduration. This results in a more sensitive overall video system andallows the aperture to be comparatively smaller for a given lightingsituation than with prior art shutters. The smaller aperture means afaster shutter speed, hence greater clarity and less blurring of fastmoving objects.

Furthermore, since rotation of the disks is counterclockwise (as viewedfrom the lense side), the unique shape of openings 56 and 58 cause thelower left corner 498 of rectangular area 488 to be swept first withillumination. Since this lower left corner is also first to beinterrogated by the electron beam in the raster scanning pattern, theoptical image is captured in the same sequence as it illuminates thepickup device. Hence any image decay occurs evenly across the entirepickup device.

While the invention has been described in its presently preferredembodiments, various changes in the details, materials, and arrangementof parts may be made by those skilled in the art within the principlesand scope of the invention and defined in the appended claims.

What is claimed is:
 1. A focal plane shutter for a video camera having alense and pickup comprising:disk means positioned between said lense andsaid pickup for rotation about an axis to define an annular locus inregistration with said pickup, said disk means having light admittingaperture means intersecting said locus, means for substantiallybalancing said disk means during rotation, said means for balancingcomprising at least one recessed relief area means formed in said diskmeans and not extending entirely through said disk means, and means forrotating said disk means.
 2. The shutter of claim 1 wherein said diskmeans comprises a first disk member and a second disk member bothrotatable about a common axis and only one light admitting aperturemeans is provided in each disk member.
 3. The shutter of claim 2 whereinsaid first and second disk member each have openings in registrationwith said locus which cooperate to define said light admitting aperturemeans.
 4. The shutter of claim 1 wherein said means for balancing saiddisk means renders substantially zero the polar movement of inertia ofsaid disk means.
 5. The shutter of claim 2 further comprising means forbalancing each of said first and second disk members.
 6. The shutter ofclaim 5 wherein said means for balancing comprises a recessed reliefarea means formed in said first disk member and one or more aperturesformed in said second disk member.
 7. A shutter for a video camera ofthe type which scans a raster with periodic retraces in accordance withclaim 1 further comprising means for rotating said disk means insynchronism with said retraces.
 8. The shutter of claim 1 wherein saidmeans for rotating said disk means rotates said disk means at nominally3600 revolutions per minute.
 9. A focal plane shutter mechanism for avideo camera having a light sensing pickup comprising:first disk meansand second disk means disposed in said camera for rotation about anaxis, each of said first and second disk means having light admittingaperture means, said first disk means having a recessed relief areameans formed therein to counterbalance its light admitting aperturemeans, said relief area means extending only partially through said diskmeans, and said second disk means having means for counterbalancing itslight admitting aperture means.
 10. The shutter of claim 9 wherein saidmeans for counterbalancing said second disk means comprises one or moreopenings formed in said second disk means.
 11. The shutter of claim 9wherein said means for counterbalancing said second disk means comprisesa recessed relief area means extending only partially through saidsecond disk means.
 12. A shutter for a video camera of the type whichscans a raster with periodic retraces in accordance with claim 9 furthercomprising means for rotating said disk means in synchronism with saidretraces.
 13. The shutter of claim 9 further comprising means forrotating said first and second disk means.
 14. The shutter of claim 13wherein said means for rotating said disk means rotates said first andsecond disk means at nominally 3600 revolutions per minute, and whereinsaid first and second disk means are disposed relative to said pickup toat all times block light from reaching said pickup, except during asingle uninterrupted interval occurring not more than once eachrevolution of said first and second disk means and lasting for less thanthe period of revolution.
 15. The shutter of claim 9 wherein saidrecessed relief area means has stiffening means therein.
 16. The shutterof claim 11 wherein said recessed relief area means on said second diskmeans has stiffening means therein.
 17. A focal plane shutter mechanismfor a video camera having a lense and pickup, said mechanismcomprising:disk means positioned between said lense and said pickup forrotation about an axis to define an annular locus in registration withsaid pickup; said disk means having a single light admitting apertureintersecting said locus; said disk means, except for said aperture,being opaque to the passage of light between said lense and said pickup;said disk means comprises first and second disk means rotatable about acommon axis; means for rendering substantially zero the polar moment ofinertia of said disk means; said means for rendering substantially zerothe polar moment of inertia comprising at least one recessed reliefarea, said recessed relief area formed in said disk means and notextending entirely through said disk means; and means for rotating saiddisk means.
 18. The shutter mechanism as set forth in claim 17 whereinsaid means for rendering substantially zero the polar moment of inertiafurther includes one or more openings formed in one of said first andsecond disk means.
 19. The shutter mechanism as set forth in claim 18wherein a first opening is formed in said first disk means and arecessed relief area is formed in said second disk means.
 20. Theshutter mechanism as set forth in claim 17 wherein said first and seconddisk means each have a single opening and said openings are inregistration with said locus and cooperate to define said lightadmitting aperture.
 21. The shutter mechanism as set forth in claim 17wherein said means for rotating said disk means comprises a direct drivemechanism.
 22. The shutter mechanism as set forth in claim 17 furthercomprising means for synchronizing the positioning of said lightadmitting aperture relative to said pickup during rotation of said diskmeans.
 23. The shutter mechanism as set forth in claim 17 wherein eachof said first and second disk means have only a single light admittingaperture.
 24. The shutter mechanism as set forth in claim 17 whereinsaid video camera scans a raster with periodic retraces and said shuttermechanism further comprises means for rotating said disk means insynchronism with said retraces.
 25. The shutter mechanism as set forthin claim 17 wherein said means for rotating said disk means rotates saiddisk means at nominally 3600 revolutions per minute.
 26. The shuttermechanism as set forth in claim 17 further comprising means foradjusting the size of said light admitting aperture.
 27. The shuttermechanism as set forth in claim 17 wherein the size of said lightadmitting aperture is adjustable to achieve a shutter speed in the rangefrom 1/250 of a second to 1/20,000 of a second.
 28. A shutter mechanismfor a video camera of the type which scans a raster with periodicretraces, said video camera having a lense and pickup device forming afocal plane, said improvement comprising:a first disk positioned betweensaid lense and said pickup device and having an axis of rotation offsetfrom said focal plane; a second disk positioned adjacent said first diskand having a common axis of rotation with said first disk; said firstdisk having a single light admitting aperture intersecting said focalplane when said first disk is rotating; said second disk having a singlelight admitting aperture intersecting said focal plane when said seconddisk is rotating; first balancing means for substantially balancing saidfirst disk means, said first balancing means comprising a recessedrelief area not extending through said first disk means; secondbalancing means for substantially balancing said second disk means; saidlight admitting apertures of said first and second disk means being inregistration to form an angular opening in said focal plane once perrevolution of said first and second disk means; said first and seconddisk means except for said light admitting apertures not permitting thepassage of light between said lense and said pickup device; means foradjusting the size of said angular opening; drive means for rotatingsaid first and second disk means about said axis of rotation atnominally 3600 revolutions per minute; and means for synchronizing therotation of said first and second disk means and the positioning of saidangular opening in said focal plane with said periodic retraces.
 29. Theshutter mechanism as set forth in claim 28 wherein said second balancingmeans comprises a recessed relief area on said second disk means. 30.The shutter mechanism as set forth in claim 28 wherein said first diskmeans has a first surface uninterrupted except for said light admittingaperture and wherein said first disk means is positioned with said firstsurface facing said pickup device.
 31. The shutter mechanism as setforth in claim 28 wherein the polar moments of inertia of said first andsecond disk means are rendered substantially zero by said first andsecond balancing means.
 32. The shutter mechanism as set forth in claim28 wherein said drive means comprises a direct drive mechanism.
 33. Theshutter mechanism as set forth in claim 28 wherein the size of saidangular opening is adjustable to achieve a shutter speed on the order of1/20,000 of a second.
 34. A focal plane shutter mechanism for a videocamera of the type which scans a raster with periodic retraces and has alight sensing pickup, said improvement comprising:disk means positionedon said camera and comprising first and second disk means rotatableabout a common axis; each of said first and second disk means having asingle light admitting aperture and balancing means; said balancingmeans comprising recessed relief area, said recessed relief areas formedin said disk means and not extending entirely through said disk means;and said disk means being disposed relative to said pickup at all timesto block light from reaching said pickup, except during a singleuninterrupted interval occurring not more than once each revolution ofsaid disk means and lasting for less than the period of revolution;rotation means for rotating said disk means; and means for synchronizingthe rotation of said disk means and the positioning of said lightadmitting apertures relative to said pickup and said periodic retraces.35. The shutter mechanism of claim 34 wherein said rotation meansrotates said disk means at nominally 3600 revolutions per minute andwherein said light admitting apertures define an angular opening whichis adjustable to achieve shutter speeds on the order of 1/20,000 of asecond.
 36. The shutter mechanism of claim 34 wherein said means forsynchronizing includes reflector means on said disk means and sensormeans on said camera.
 37. A focal plane shutter for a video camerahaving a lense and pickup comprising:disk means positioned between saidlense and said pickup for rotation about an axis to define an annularlocus in registration with said pickup, said disk means having lightadmitting aperture means intersecting said locus, said light admittingaperture means positioned on said disk means such that two sides of saidaperture means are bound by a pair of intersecting lines generating froma point offset a predetermined distance from the geometric center ofsaid disk means, means for substantially balancing said disk meansduring rotation, said means for balancing comprising at least oneweighted means attached to said disk means, and means for rotating saiddisk means.
 38. The shutter of claim 37 wherein said disk meanscomprises a first disk member and a second disk member both rotatableabout a common axis and only one light admitting aperture means isprovided in each disk member.
 39. The shutter of claim 38 wherein saidfirst and second disk member each have openings in registration withsaid locus which cooperate to define said light admitting aperturemeans.
 40. The shutter of claim 37 wherein said means for balancing saiddisk means renders substantially zero the polar moment of inertia ofsaid disk means.
 41. The shutter of claim 38 further comprising meansfor balancing each of said first and second disk members.
 42. Theshutter of claim 41 wherein said means for balancing comprises aweighted means secured to said first disk member and one or moreapertures formed in said second disk member.
 43. A focal plane shuttermechanism for a video camera having a light sensing pickupcomprising:first disk means and second disk means disposed in saidcamera for rotation about an axis, each of said first and second diskmeans having light admitting aperture means, said light admittingaperture means positioned on said disk means such that two sides of saidaperture means are bound by a pair of intersecting lines generating froma point offset a predetermined distance from the geometric center ofsaid disk means, said first disk means having a weighted means securedthereto to counterbalance its light admitting aperture means, saidweighted means being positioned adjacent said light admitting aperturemeans, and said second disk means having means for counterbalancing itslight admitting aperture means.
 44. A focal plane shutter mechanism fora video camera having a lense and pickup, said mechanism comprising:diskmeans positioned between said lense and said pickup for rotation aboutan axis to define an annular locus in registration with said pickup;said disk means having a single light admitting aperture intersectingsaid locus, said light admitting aperture means positioned on said diskmeans such that two sides of said aperture means are bound by a pair ofintersecting lines generating from a point offset a predetermineddistance from the geometric center of said disk means, said disk means,except for said aperture, being opaque to the passage of light betweensaid lense and said pickup; said disk means comprises first and seconddisk means rotatable about a common axis; means for renderingsubstantially zero the polar moment of inertia of said disk means; saidmeans for rendering substantially zero the polar moment of inertiacomprising at least one weighted means, and means for rotating said diskmeans.
 45. The shutter mechanism as set forth in claim 44 wherein saidmeans for rendering substantially zero the polar moment of inertiafurther includes one or more openings formed in one of said first andsecond disk means.
 46. The shutter mechanism as set forth in claim 44wherein said means for rendering substantially zero the polar moment ofinertia further includes at least one recessed relief area formed in oneof said first and second disk means.